Melt electrowritten scaffolds containing fluorescent nanodiamonds for improved mechanical properties and degradation monitoring

Biocompatible fluorescent nanodiamonds (FNDs) were introduced into polycaprolactone (PCL) – the golden standard material in melt electrowriting (MEW). MEW is an advanced additive manufacturing technique capable of depositing high-resolution micrometric fibres. Due to the high printing precision, MEW finds growing interest in tissue engineering applications. Here, we introduced fluorescent nanodiamonds (FNDs) into polycaprolactone prior to printing to fabricate scaffolds for biomedical applications with improved mechanical properties. Further FNDs offer the possibility of their real-time degradation tracking. Compared to pure PCL scaffolds, the functionalized ones containing 0.001 wt% of 70 nm-diameter nanodiamonds (PCL-FNDs) showed increased tensile moduli (1.25 fold) and improved cell proliferation during 7-day cell cultures (2.00 fold increase). Furthermore, the addition of FNDs slowed down the hydrolytic degradation process of the scaffolds, accelerated for the purpose of the study by addition of the enzyme lipase to deionized water. Pure PCL scaffolds showed obvious signs of degradation after 3 h, not observed for PCL-FNDs scaffolds during this time. Additionally, due to the nitrogen-vacancy (NV) centers present on the FNDs, we were able to track their amount and location in real-time in printed fibres using confocal microscopy. This research shows the possibility for high-resolution life-tracking of MEW PCL scaffolds’ degradation.